In the mammalian species studied to date, it is established that there are two general types of ameloblasts in the enamel organ during the maturation stage of enamel formation: ruffled-ended (R-A) and smooth-ended (S-A). The functions of these respective types of cells have not have been determined. Reports from our laboratories and from other groups suggest that the sequentially modulating cell types may be involved in various ion transport activities. We have recently reported on methods by which the relationship between the respective cell types, 45Ca uptake patterns in the enamel, and staining characteristics of the enamel can be established. These methods and others will be applied in an effort to gain insight into the functions of the R-A and S-A ameloblasts, particularly with regard to ion transport activities. The proposed specific aims are as follows: (1) to conduct lanthanum perfusion studies on the rat to determine the permeability to calcium of the extracellular channels between the R-A and the S-A ameloblasts; 2) to define the structure of the maturation stage bovine enamel organ, with particular attention directed to identification of ameloblast cell types; (3) to study the solubility of cow enamel under the bands of R-A and S-A ameloblasts by application of various concentrations of acid or EDTA to the enamel surface, and observation of the result under the dissecting microscope and the scanning electron microscope; (4) to assay the nitrogen, fluorine, and phosphorus content of the surface enamel of bovine incisors under the sequential bands of R-A and S-A ameloblasts using proton activation analysis; and (5) to assay enamel samples taken from under the alternating bands of R-A and S-A ameloblasts for phosphorus, protein, and fluoride content using chemical methods; and to determine the amelogenin and enamelin content of such samples. The findings should provide information on which hypotheses can be based to explain the functions of the two cell types and the mechanisms involved in such functions. Systematic testing of such hypotheses would be pursued in subsequent studies.